The present invention relates to a brake fluid pressure adjustment apparatus possessing antiskid control action for use in brake apparatuses of vehicles, which prevents locking of vehicle wheels during braking.
Prior Art
FIG. 12 shows a brake fluid pressure adjustment apparatus possessing antiskid control action for use in brake apparatuses of vehicles, which prevents locking of the wheels during braking (Japanese Patent Application First Publication No. Hei 1-297350; U.S. Pat. No. 4,988,148). This brake fluid pressure control apparatus 261 employs a flow control valve possessing a casing 258 and a spool 259. In casing 258, a master cylinder communication port 251, a wheel cylinder communication port 253, and a reservoir communication port 257 are provided. Master cylinder communication port 251 is communicated to a master cylinder 250, wheel cylinder communication port 253 is communicated to a wheel cylinder 252, and reservoir communication port 257 is communicated to the intake side of pump 256 and reservoir 255 via first valve 254. Furthermore, pump 256 takes in and discharges brake fluid inside of the reservoir 255. Spool 259 is provided in a manner such that it is movable within casing 258.
Spool 259 of flow control valve 260 communicates master cylinder communication port 251 and wheel cylinder communication port 253 during non-action of antiskid control. Additionally, spool 259 moves by means of the difference in pressure created due to the opening of first valve 254 at the time of pressure reduction during antiskid control, and limits the communication of master cylinder communication port 251 and wheel cylinder communication port 253, while at the same time connecting wheel cylinder communication port 253 and reservoir 257. At the same time, spool 259 supplies to wheel cylinder 252 brake fluid which is returned by means of pump 256, through the closing of the aforementioned first valve 254 during repressurization.
Brake fluid pressure adjustment apparatus 261 is constructed in a manner such that at the time of repressurization of brake fluid pressure during antiskid action, the pulsating motion generated by pump 256 and the stroke fluctuations (so-called "kick-back") created in master cylinder 250 are both prevented. That is, the brake fluid discharged by pump 256, with no relation to master cylinder 250, passes via flow control valve 260 at a fixed flow amount, flowing out towards wheel cylinder 252. As a result, casing 258 possesses, individually, pump communication port 262 connecting to the discharge side of pump 256. Additionally, during antiskid control, spool 259 limits the communication between pump communication port 262 and master cylinder communication port 251. Together with this, a channel 263, separate from flow control valve 260, is provided between master cylinder communication port 251 and pump communication port 262 in a manner so that brake fluid is returned at a fixed flow amount from pump 256 to master cylinder 250; in this channel 263, an orifice 264 is provided. However, in the above-mentioned construction of brake fluid pressure adjustment apparatus 261, when the aforementioned orifice 264 between master cylinder communication port 251 and pump communication port 262 is large, a large pump pulsation is imparted to master cylinder 250. Additionally, when orifice 264 is too small, there exist problems during manufacturing, such as increased processing costs, as well as problems such as gum, mixed into the brake fluid, becoming clogged at orifice 264. Furthermore, orifice 264 varies the flow amount of brake fluid returned to master cylinder 250 due to fluctuation in the discharge pressure of pump 256. As a result, a stroke fluctuation is created by master cylinder 250. Therefore, in regard to the above points, improvements have become necessary.